Nations seek to produce biofuels and biochemicals from farm crops for economic, environmental and national security reasons. Sugar cane is currently the world's lowest-cost raw material for the production of biomass energy and biochemicals. The crop can produce high yields of sugar and fiber at relatively low agricultural costs. However, sugar cane cannot be rotated with food crops or even grown in many areas of the world, including those with degraded, infertile land or arid lands with low rainfall or with short growing and harvesting seasons (less than 180 days). Nations want to use these lands in way that doesn't compete with food crops.
Many nations could potentially use a similar, but lower input, cane sugar crop called sweet sorghum, which can grow on arid, saline and alkaline soils in about 120 days. Compared to sugar cane, sweet sorghum can produce nearly as much sugar and fiber with lower agricultural costs, including seeds, nitrogen fertilizer, water and land. However, pest problems can make it difficult to grow sweet sorghum in southern areas with long growing and harvesting seasons. Generally pests don't pose significant problems in colder, northern regions.
The overall problem in colder, northern regions is the production of various products from sweet sorghum is not cost-competitive when the crop must be hauled to the plant and processed only during the short harvest season. The solution is to delay deterioration of the sugars by storing the crop as a de-leafed whole plant in the cold weather near local farms to extend the hauling and process season over the winter (like accomplished by the sugar beet industry).
The storage of sugar crops depends on providing conditions that allow the crop to live at low metabolism. Sugar losses are caused by normal respiration as the stalks use sugar as an energy source at above freezing temperatures. Sugar crops respire and deteriorate more rapidly under several conditions, including: when damaged by disease or insects during growth; when burned; if the crop is cut or bruised during mechanical harvesting; if the crop is subjected to elevated temperatures above freezing; or by an accumulation of environmental or climatic effects including heat, sunlight and alternating frosts and thaws.
As practiced on a commercial scale by the sugar beet industry, storage of sugars within sugar beets outside during cold weather requires harvest as a whole plant with minimal damage in order to slow deterioration over the winter. In addition, leaf removal is also likely necessary to allow circulation of air within large commercial piles of the crop to prevent over-heating from excessive fermentation. Piles are typically sealed on the outside with hay or plastic. Poor ventilation or desiccation reduces the oxygen content in piles causing fermentation, decay and sugar loss. For successful commercial storage of sweet sorghum sugars, a harvesting system must be able to strip the leaves with minimal stalk damage.
The large surface area of the sweet sorghum leaves means pile ventilation will be blocked. Moreover, it would be preferable to reject most of the leaves back onto the land as soil conditioner and also to get them out of the way for piling and later milling. But the storage methodology practiced by the sugar beet industry, which requires removal of virtually all leaf matter back to the soil, cannot be assumed to be most effective for sweet sorghum. Stalks pile with less density and greater amount of air spaces than beets. It is unknown whether some leaves should be used to slow the air flow or if bigger piles are needed with better sealing when temperatures are cold and about to warm. At least initially, a wide range of leaf removal is preferable until sufficient data can be obtained through testing of large piles under actual variable weather conditions to determine how much leaf removal is optimal for commercial storage of sweet sorghum.
Sugar loss increases with cutting. N.J. King in Producers' Review 1972, 62, (7), 66-67 reported for sugar cane: “While full-length (6-ft) cane stalks with two cut ends dry out rapidly, the same stalks, when passed through a chopper harvester, will be cut into six 12 inch billets having a total of 12 ends which do not dry rapidly because of the protection afforded by surrounding billets. The result is faster deterioration than in the case of the 6-ft stalks, the rate increasing with reduction in billet size, short billets also splitting more easily than long ones and thus being susceptible to attacks by bacteria.”
Unfortunately, commercial harvesting systems for sweet sorghum are not currently available that can strip the leaves from stalks with minimal damage. Sweet sorghum can be harvested, handled and processed with equipment used for sugar cane (since both are similarly-shaped cane sugar crops). But commercial sugar cane harvesters, including both choppers and soldiers, are also not designed to strip the leaves with minimal damage even though it would be advantageous. Nor is there commercial equipment available for either pre-harvest or post-harvest that could strip the leaves from stalks of either sweet sorghum or sugar cane with minimal damage.
Commercial chopper (billet) harvesters are used by most commercial sugar cane operations and are also proposed by most sweet sorghum projects, especially those in warmer southern climates. Sugar cane chopper harvesters can strip the leaves to the farm field, handle fairly narrow rows and recover lodged stalks, but the chopping into billets damages the stalks far too much for long-term storage in colder northern climates.
Commercial soldier (whole stalk) harvesters can harvest sugar cane stalks with little damage, even though the chains on which the stalks ride may cause excessive damage. But commercial soldier harvesters are being phased out for use with sugar cane and also have little use for sweet sorghum, because these whole stalk harvesters cannot strip the leaves, and thus require burning of the leaves in the field, which may be prohibited in some areas. Burning also causes infections and loss of sugars. Moreover, crop yields cannot be maximized because the harvesters cannot handle narrow row spacing or harvest lodged stalks fallen by heavy crop weights.
Some researchers have proposed pre-harvest leaf removal using high-boys, driven above the crop with the wheels between the rows, and equipped with circulating rubber finger strippers that beat the leaves off the stalks from both sugar cane and sweet sorghum stalks standing in the field. But these machines cannot remove leaves from lodged stalks and appear to considerably damage the stalks; while the rubber strippers wear out too quickly for commercial use. Some commercial sugar cane operations, especially in Cuba, use stationary sugar cane cleaning tables that can strip leaves, but this requires cutting, and thus damaging, the stalks.
A few sugar cane prototype harvesters have been built to harvest whole stalks of sugar cane with minimal damage while stripping the leaves. Such harvesters also tend to be designed for the stalks to ride on a conveyor, instead of chains, to minimize stalk damage and also to harvest narrow rows and lodged stalks. But these prototype sugar cane harvesters have not been fully developed for commercial harvesting of sugar cane, and until now, have not been modified for, or tested on, sweet sorghum.
Besides the essential need to strip the leaves with minimal damage, modification of sugar cane harvesters for use with sweet sorghum must also address some crop differences. For example, sweet sorghums often have more numerous, thinner and softer stalks, less numerous and shorter leaves, and grain heads, compared to sugar cane. The present invention provides a solution to these needs and other problems, and offers other advantages over the prior art.
Research has indicated that very low sugar losses may be had within one meter high piles of de-leafed and whole sweet sorghum stalks stored outdoors on a farm field in southern Minnesota during the winter. In order to provide for optimal storage and processing conditions with the least amount of sugar deterioration, sorghum should be de-leafed in the field, with minimal damage to the stalk, prior to transport to processing plants. This invention solves this, and other, problems and provides advantages over the prior art.
The specific problem addressed by these inventive changes is the lack of a harvester that can economically deliver sweet sorghum as de-leafed and undamaged whole stalks required for storage of the crop in climates with cold winters, while also meeting other requirements including the minimization of manual labor through economy-of-scale and mechanization, and also yield maximization through the harvesting of narrow rows (30 to 40 inches), cutting the stalks at ground level and recovering fallen stalks.
The proposed solution is to modify a harvester that has been designed to meet these requirements for the somewhat similar crop sugar cane (whose sugars can also be stored albeit for shorter periods in warmer climates), and these modifications represent the novelty of the invention.